Current Metagame

Hello all! I am a returning player. I stopped anything related to SC2 a few years ago (before HotS launched), but now I have a huge drive to continue playing this game and having fun.

The problem here is that it is a little hard to quickly get back into a good rhythm, and figure out what is the general metagame nowadays. I'd like to learn a thing or two, so I don't get stomped. I am also curious to know the general consensus on balance, and things like that.